Call access control method

ABSTRACT

The present invention discloses a call access control (CAC) method applicable to call access during call initiation and cell switching in TDD-CDMA mobile communication system. The method comprises: counting the number of accessed subscribers in all current communication time slots of the home base station for an access request from a new subscriber, to determine channel resource occupations in different time slots; comparing the channel resource occupations in the different time slots, and then allocating idle resource units in the time slots having available channel resources and the minimum number of accessed subscribers to the subscriber sending the access request. The present invention achieves dynamic allocation of channel resources in cells and have an advantage of simple implementation and applicability.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a National Phase of International Application SerialNo. PCT/CN03/00548, filed Jul. 10, 2003.

FIELD OF THE INVENTION

The present invention relates to a method of dynamic allocation of radiochannel resources in mobile communication field, particularly to a callaccess control method during call initiation or cell switching in TDDCDMA mobile communication system.

BACKGROUND OF THE INVENTION

For 3G mobile communication systems, the call access control policy putforth in the standard document mainly uses a concentrated call accesscontrol algorithm in RNC to allocate channel resources according to thecurrent load of the communication system as well as QoS demands of thecalling subscriber. Since the processing and implementation of theconcentrated call access control algorithm is in the RNC, which is on ahigher level in the mobile network hierarchy, sophisticated signalingsupport between RNC and UE and between RNC and Node_B in the system isrequired. Therefore, the algorithm is complex in operation and difficultto implement.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a simple and effectivecall access control method based on counting of accessed subscriber, toimplement dynamic allocation of channel resources of the base station.

The technical solution of the present invention is applicable to callaccess control during call initiation and cell switching, comprising thefollowing steps:

1) counting the number of accessed subscribers in all currentcommunication time slots of the home base station for an access request,to determine channel resource occupations in different time slots;

2) comparing said channel resource occupations in the different timeslots, and then allocating idle resource units in the time slots havingavailable channel resources and the minimum number of accessedsubscribers to the subscriber sending the access request.

In said technical solution:

Said access request is a call access request sent from a new mobilesubscriber to the home base station or a call switching request sentfrom a mobile subscriber to its adjacent cells.

Said counting in step 1) refers to: arranging corresponding counters fordifferent time slots respectively, so that the number of counters areequal to the maximum number of communication time slots that can besupported by the base station; counting accessed subscribers in the timeslots, and increasing the corresponding counter by 1 if the currentresource unit is occupied; otherwise increasing it by 0.

Step 2) comprises:

a) comparing channel resource occupations in all uplink time slots, andallocating the idle resource unit in uplink time slots having availablechannel resource and the minimum number of accessed subscribers to thenew subscriber sending the access request as an uplink channel; if theidle resource unit is allocated successfully, going to step b),otherwise going to step c);

b) comparing channel resource occupations in all downlink time slots,and allocating the idle resource unit in downlink time slots havingavailable channel resources and the minimum number of accessedsubscribers to the new subscriber sending the access request as adownlink channel;

c) returning a response signal to the call access request according tothe channel resource allocations in the uplink and downlink time slots.

Step a) comprises:

comparing all counters storing the count value of accessed subscribersin the uplink time slots one by one, and selecting a counter with theminimum count value in the uplink time slots;

comparing said count value in the counter with the threshold (i.e., themaximum number) of subscribers to be accessed per time slot supported bythe base station; if the count value stored in the counter is smallerthan the threshold, allocating an idle resource unit in the uplink timeslots corresponding to the counter as an uplink channel to the newsubscriber sending the access request; otherwise indicating the failedallocation.

Step b) comprises:

comparing all counters storing the count value of accessed subscribersin the downlink time slots one by one, and selecting a counter with theminimum count value in the downlink time slots;

comparing said count value in the counter with the threshold (i.e., themaximum number) of subscribers to be accessed per time slot supported bythe base station; if the count value stored in the counter is smallerthan the threshold, allocating an idle resource unit in the downlinktime slots corresponding to the counter as a downlink channel to the newsubscriber sending the access request; otherwise indicating the failedallocation.

Step c) refers to: when the channel resources in the uplink and downlinktime slots are both allocated successfully, returning a message to themobile station sending the access request to indicate the succeededaccess, or returning a message to the mobile station sending the cellswitching request to indicate the succeeded cell switching; otherwisereturning a message to the mobile station sending the access request toindicate the failed access, or returning a message to the mobile stationsending the cell switching request to indicate the failed cellswitching.

The threshold (i.e., the maximum number) of subscribers to be accessedper time slot supported by the base station is 6˜8, and is determinedduring initialization.

Compared with the concentrated call access control algorithm implementedin the RNC at higher level, the method of the present invention isimplemented in the home base station processing a call access requestsending from a subscriber, and the allocation of channel resources canbe performed flexibly in a local area, simplifying signaling switchinggreatly. The implementation of the method is relatively simple anddoesn't require complex operation. With the method, channel resourceswith lower system interference may be allocated dynamically tosubscribers sending the call request. Since the present invention alsotakes account into interference from other cells and maintains aneffective call access control (CAC) threshold N, so as to reduceinterference of new subscribers to the system and guarantee QOS demandof subscribers to be accessed; therefore, it can improve system capacityeffectively.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart of the call access control method of the presentinvention.

DETAILED DESCRIPTION OF THE EMBODIMENT

The embodiment is described taking the access call initiated by a newmobile subscriber to the home base station as an example.

The method of the present invention comprises: counting the number ofaccessed subscribers in all current communication time slots of the homebase station for an access request, to determine channel resourceoccupations in different time slots; then comparing said channelresource occupations in the different time slots, and then allocatingidle resource units in the time slots having available channel resourcesand the minimum number of accessed subscribers to the subscriber sendingthe access request. Therefore, dynamic allocation of base stationchannel resources can be implemented.

For example, in the low data rate (1.28 Mchips) TD-SCDMA mobilecommunication system as shown in FIG. 1, it is set that there aretotally 7 uplink and downlink time slots available for communication.When the flow shown in FIG. 1 is applied to a high data rate (3.84Mchips) TDD system, the total number of uplink and downlink time slotsmay be modified to 15; Cij in the flow chart represents the state ofcurrent channels being searched (may be 0 or 1, 0 for idle, and 1 foroccupied); TSi represents time slot number; STSi represents the counterused to count accessed subscribers corresponding to time slot TSi; Nrepresents the threshold (i.e., the maximum number) of subscribers to beaccessed per time slot.

A sub-frame in TD-SCDMA comprises 7 time slots for communication, whichare used to transfer uplink (UL) and downlink (DL) traffic; according toa protocol, a time slot can support up to 16 subscriber channelssimultaneously; thus a carrier frequency/time slot/channel constitutes aresource unit (RU); under interference from other cells, the Call AccessControl (CAC) access threshold N (i.e., the maximum number) ofsubscribers to be accessed in a time slot must be smaller than themaximum number of channels that are supported in a current time slot. Asa design parameter, threshold N may be adjusted as required in systemdesign (6˜8 is preferred) and is determined during initialization.

Please see the flow chart shown in FIG. 1, when a new subscriber is tobe added, the home base station that receives the access requestsearches the state of channel resources in the 7 time slots and performscounting for channel occupation in all uplink and downlink time slots.Corresponding counters is arranged for different time slots and storesthe subscriber counting result. If a resource unit is occupiedcurrently, it increases the counter by 1; if the resource unit is idle,it increases the counter by 0. After obtaining the statistical results,the base station compares the statistical results in the uplink (UL)time slots, and, on the premise that the counter value is lower than theCall Access Control (CAC) access threshold N, it allocates the channelresource unit in the uplink time slots with the minimum count value asan uplink channel resource to the requesting subscriber. After theuplink channel resource is allocated successfully, it controls theallocation of channel resource in downlink time slots. It compares thestatistical result in downlink (DL) time slots, and, on the premise thatthe counter value is lower than the Call Access Control (CAC) accessthreshold N, it allocates the channel resource unit in the downlink timeslots with the minimum counter value as a downlink channel resource tothe requesting subscriber, so that the time slots with the minimumco-channel interference are allocated to the new calling subscriber, toimplement dynamic radio resource allocation.

In allocation principle described above, the Call Access Control (CAC)is successful only when both uplink and downlink meet the constraintconditions, and in this case, the base station will return a message tothe requesting mobile station to indicate the access is successful;otherwise the base station will return a message to the requestingmobile station to indicate the failed access. In the call access controlmethod of the present invention, the selection of the threshold N ofsubscribers to be accessed is crucial; the base station that performsresource searching and allocation must maintain an effective CAC accessthreshold N; whereas the threshold (i.e., the maximum number) ofsubscribers to be accessed per time slot N is the result of compromisingbetween GoS (Grade Of Service) and QoS (Quality Of Service). Underinterference from other cells, the threshold N of subscriber to beaccessed must be lower than the maximum number of channels that can besupported by the current time slot.

The method of the present invention is applicable to not only the accesscall of a new subscriber but also the switching call between adjacentcells; whatever the call is, it involves searching for and allocatingchannel resources and has no essential difference in regard to the callaccess control (CAC) principle. When a mobile subscriber in callingmoves into an adjacent cell, the home cell changes. To meet therequirement for call quality and level, the mobile subscriber will senda switching call request to the current home cell; when receiving theswitching call request, the current home cell executes the same methodand steps as those for the access call of a new mobile subscriberinitiated to a home base station; if the channel resources are allocatedsuccessfully, the home base station returns a message to the mobilesubscriber to indicate the succeeded switching call access; otherwise itreturns a message to indicate the failed switching call access.

1. A call access control method during call initiation or cell switchingin a TDD CDMA mobile communication system, comprising the followingsteps: (1) counting the number of accessed subscribers in all currentcommunication time slots of a home base station for an access request,to determine channel resource occupations in different time slots; and(2) comparing said channel resource occupations in the different timeslots, and then allocating idle resource units, in the time slots havingavailable channel resources and a minimum number of accessedsubscribers, to the subscriber sending the access request.
 2. The methodaccording to claim 1, wherein said access request in step (1) refers toan access call sent from a new mobile subscriber to the home basestation.
 3. The method according to claim 1, wherein said access requestin step (1) refers to a switching call sent from a mobile subscriber toadjacent cells.
 4. The method according to claim 1, wherein the countingin step (1) comprises: arranging corresponding counters for differenttime slots respectively, so that the number of counters are equal to themaximum number of time slots for communication that can be supported bythe base station; counting accessed subscribers in the time slots, andincreasing the corresponding counter by 1 if the current resource unitis occupied; otherwise increasing it by
 0. 5. The method according toclaim 1, wherein step (2) comprises: a) comparing channel resourceoccupations in all uplink time slots, and allocating the idle resourceunit in uplink time slots having available channel resource and theminimum number of accessed subscribers to the new subscriber sending theaccess request as an uplink channel; if the idle resource unit isallocated successfully, going to step b), otherwise going to step c); b)comparing channel resource occupations in all downlink time slots, andallocating the idle resource unit in downlink time slots havingavailable channel resources and the minimum number of accessedsubscribers to the new subscriber sending the access request as adownlink channel; c) returning a response signal to the call accessrequest according to the channel resource allocations in the uplink anddownlink time slots.
 6. The method according to claim 5, wherein step a)comprises: comparing all counters storing the count value of accessedsubscribers in the uplink time slots one by one, and selecting a counterwith the minimum count value in the uplink time slots; comparing saidcount value in the counter with the threshold of subscribers to beaccessed per time slot supported by the base station; if the count valuestored in the counter is smaller than the threshold, allocating an idleresource unit in the uplink time slots corresponding to the counter asan uplink channel to the new subscriber sending the access request;otherwise indicating the failed allocation.
 7. The method according toclaim 5, wherein step b) comprises: comparing all counters storing thecount value of accessed subscribers in the downlink time slots one byone, and selecting a counter with the minimum count value in thedownlink time slots; comparing said count value in the counter with thethreshold of subscribers to be accessed per time slot supported by thebase station; if the count value stored in the counter is smaller thanthe threshold, allocating an idle resource unit in the downlink timeslots corresponding to the counter as a downlink channel to the newsubscriber sending the access request; otherwise indicating the failedallocation.
 8. The method according to claim 6, wherein the threshold ofsubscribers to be accessed per time slot supported by the base stationis 6˜8, and is determined during initialization.
 9. The method accordingto claim 7, wherein the threshold of subscribers to be accessed per timeslot supported by the base station is 6˜8, and is determined duringinitialization.
 10. The method according to claim 5, wherein step c)refers to: when the channel resources in the uplink and downlink timeslots are both allocated successfully, returning a message to the mobilestation sending the access request to indicate the succeeded access;otherwise returning a message to the mobile station sending the accessrequest to indicate the failed access.
 11. The method according to claim5, wherein the channel resources in the uplink and downlink time slotsare both allocated successfully, or returning a message to the mobilestation sending the cell switching request to indicate the succeededcell switching; otherwise returning a message to the mobile stationsending the cell switching request to indicate the failed cellswitching.
 12. The method of claim 6 wherein said threshold ofsubscribers is a maximum number of subscribers.
 13. The method of claim7 wherein said threshold of subscribers is a maximum number ofsubscribers.
 14. The method of claim 8 wherein said threshold ofsubscribers is a maximum number of subscribers.
 15. The method of claim9 wherein said threshold of subscribers is a maximum number ofsubscribers.
 16. A base station in a TDD CDMA mobile communicationsystem, comprising: a first unit adapted to count the number of accessedsubscribers in all current communication time slots of the base stationin response to an access request to determine channel resourceoccupations in the time slots; a second unit adapted to compare saidchannel resource occupations in the time slots and allocate idleresource units in the time slots that have available channel resourcesand a minimum number of accessed subscribers to the subscriber.
 17. Thebase station according to claim 16, wherein said access request is anaccess call sent from a mobile subscriber to the base station.
 18. Thebase station according to claim 16, wherein said access request is aswitching call sent from a mobile subscriber to adjacent cells.
 19. Thebase station according to claim 16, wherein said counting the number ofaccessed subscribers comprises: arranging corresponding counter fordifferent time slot respectively, so that the number of the countersequals to the maximum number of time slots for communication that can besupported by the base station; and counting accessed subscribers in thetime slots, and increasing the corresponding counter by 1 if the currentresource unit is occupied.
 20. The base station according to claim 16,wherein said comparing said channel resource occupations and allocatingidle resource units comprises: comparing channel resource occupations inall uplink time slots, and allocating the idle resource unit in uplinktime slot, that has available channel resource and the minimum number ofaccessed subscribers, to a subscriber that sent the access request as anuplink channel; and if the idle resource unit is allocated successfully,comparing channel resource occupations in all downlink time slots, andallocating the idle resource unit in the downlink time slot, that hasavailable channel resources and the minimum number of accessedsubscribers, to the subscriber that sent the access request as adownlink channel; otherwise returning a response signal to the callaccess request according to the channel resource allocations in theuplink and downlink time slots.
 21. The base station according to claim20, wherein said comparing channel resource occupations in all uplinktime slots and said allocating the idle resource unit in the uplink timeslot comprises: comparing all counters storing the count value ofaccessed subscribers in the uplink time slots, and selecting a counterwith the minimum count value; and comparing said count value with athreshold, and, if the count value is smaller than the threshold,allocating an idle resource unit in the uplink time slot correspondingto the counter as an uplink channel to the subscriber that sent theaccess request, wherein the threshold is a number of subscribers to beaccessed per time slot supported by the base station.
 22. The basestation according to claim 20, wherein said comparing channel resourceoccupations in all downlink time slots and allocating the idle resourceunit in the downlink time slot comprises: comparing all counters storingthe count value of accessed subscribers in the downlink time slots, andselecting a counter with the minimum count value in the downlink timeslots; and comparing said count value in the counter with the thresholdof subscribers to be accessed per time slot supported by the basestation, and, if the count value stored in the counter is smaller thanthe threshold, allocating an idle resource unit in the downlink timeslot corresponding to the counter as a downlink channel to thesubscriber which sent the access request.
 23. The base station accordingto claim 20, wherein said returning a response signal to the call accessrequest according to the channel resource allocations in the uplink anddownlink time slots comprises returning a message to the mobile stationthat sent the access request to indicate the successful access when thechannel resources in the uplink and downlink time slots are bothallocated successfully, otherwise, returning a message to the mobilestation that sent the access request to indicate failed access.
 24. Thebase station according to claim 20, wherein the process of returning aresponse signal to the call access request according to the channelresource allocations in the uplink and downlink time slots compriseswhen the channel resources in the uplink and downlink time slots areboth allocated successfully, returning a message to the mobile stationthat sent the cell switching request to indicate the succeeded cellswitching, otherwise, returning a message to the mobile station thatsent the cell switching request to indicate failed cell switching.